The invention relates to medical instruments, and more specifically, to surgical instruments for removing cataracts from the eye.
A cataract is defined as any opacity in the lens or as any lenticular opacity that interferes with vision. Once visual function has been compromised by cataract the only effective means of treatment is surgery to remove the lens. Cataract is the most prevalent, visually disabling eye disease in the world. It is estimated that 30 to 45 million people in the world are blind, with cataract accounting for as much as 45% of this blindness. Cataracts were treated in the second half of the 18th century in Europe by couching or reclination. Couching was performed by piercing the sclera with a sharp lancet and then inserting a blunt instrument used to depress the lens into the vitreous. Incisional techniques for cataract extraction were first reported in the mid 18th century. Such techniques involved making a large incision in the cornea and removing the entire lens from the eye with the capsule intact (intracapsular). Many methods of intracapsular cataract extraction were subsequently developed. All of these methods require large 180 degree (12 mm) incisions which were unstable and required prolonged recovery. The quest for small incisional cataract wounds, a safe scaffolding to hold intraocular lenses and decreased postoperative complications all led to the decline in intracapsular cataract surgery in the 1970's.
Several techniques are presently employed in surgical practice for removal of cataracts from the eye. Regardless of the technique, cataract surgery requires making a small incision in the eye, and removing the cataract from the eye through this incision. Experience has shown the incision size in cataract surgery to be important. Smaller incisions result in more rapid post operative recovery and a more structurally stable eye. Today, the preferred surgical method of cataract extraction is extracapsular, either by standard extracapsular extraction or by phacoemulsification.
Standard extracapsular cataract surgery involves making an incision (4-7 mm) and either removing the cataractous nucleus intact or fragmenting the nucleus and mechanically removing the pieces through the incision. In general the smaller the incision the more fragmentation of the cataract is required to remove it from the eye. Regardless of the instruments used, the production of multiple fragments is technically more difficult and more likely to cause intraoperative complications than simple removal of a cataract though a larger incision.
In an effort to overcome the problems inherent in removing a cataract though a small incision (3-5 mm) in a safe, technically simple and cost effective way, a number of medical instruments have been developed. Some of these instruments incorporate a screw-like rotating cutting tool to break up the cataract. Banko U.S. Pat. No. 3,732,858 discloses an apparatus for removing blood clots, cataracts and other objects from the eye. This apparatus consist of a central rotating cutting element surrounded by a housing with an open end. By controlling the relative movement of the outer and inner aspects of the cutting instrument, objects engaged in the cutting end of the instrument are ground up and removed from the eye. Engaging the material to be removed from the eye is aided by differential pressure developed by a pressure control apparatus.
Banko U.S. Pat. No. 3,945,375 discloses a surgical instrument for removing tissue including a rotating fluted cutter member housed in a probe adapted for insertion into a body cavity. The instrument can supply irrigation fluid and evacuate the material after being engaged by the cutter. The cutting tool includes a shaft, a fluted drill type cutter, and a shank whose end is fastened to a holder. The holder has a partial internal bore which fits over a motor shaft.
Baehr et al., U.S. Pat. No. 3,906,954 disclose a surgical tissue macerating and removal tool with a high speed rotating cutting tip powered by an air turbine. A fluid pump is provided to evacuate macerated material and treatment fluid from the eye. Means are also provided for axially positioning the rotating cutting member.
Kerfoot, Jr. U.S. Pat. No. 3,976,077 discloses a surgical device with a rotary shaft having helical threads terminating in a cutting tip. The shalt is rotated at high speed and fluid is supplied to the cutting tip to aid in the maceration of the material being removed by the machine. The macerated material and the working fluid are withdrawn from the operative site by the pumping action of the rotating helical threads of the shaft.
Baehr et al., U.S. Pat. No. 4,061,146 disclose a surgical tissue macerating and removal tool having a rotating rod with a cutting member that resembles a screw. The tissue engaging end of the instrument also includes a tapering frusto-conical member which surrounds the rotating cutting tool. The frusto-conical member restricts rotation of captured tissue undergoing maceration.
These and other surgical instruments utilizing "screw-like" distal cutting elements have certain common characteristics. Each instrument consists of a small bore rotating cutting element whose cutting action depends on continuous physical contact between the tissue (cataract) and the cutting element. Without a secure method of capturing and holding the tissue (cataract), maintenance of continued contact between the cutting element and tissue (cataract) becomes very difficult. As a result, the unstabilized cataract can move about in the eye causing damage and lessening the efficiency of cutting. Fragments of the cataract are also free to float about inside the eye complicating their removal and increasing the likelihood of damage. Another common characteristic of these instruments is the use of a pressure differential or vacuum to aid in the removal of macerated tissue and aid in stabilizing the cataract. This arrangement can result in significant fluid flow through the eye with concomitant turbulence inside the eye with potential for intraocular damage.
Baehr et al. U.S. Pat. No. 4,061,146 addresses the problem of stabilization of the cataract by adding a frusto-conical housing surrounding the cutting element. This results in improved stabilization of the cataract against the cutting element but still allows for fragments of cataract to be thrown around inside the eye by fluid turbulence. Kramer U.S. Pat. No. 3,908,661 discloses a surgical instrument including an open-topped net or bag (much like a fishnet) mounted on a flexible frame for containing and controlling the cataract within the eye. The net is inserted into the eye and the nucleus placed within the bag. The nucleus is then removed from the eye by withdrawing the net, with enclosed nucleus, from the eye. The insertion and withdrawal of the net is facilitated by a frusto-conical sleeve that inserts into the surgical incision. By withdrawing the basket with contained cataract through the end of the sleeve, the cataract is squeezed causing a major portion of the nucleus to fall into the anterior chamber of the eye and 25% to 30% of the nuclear material being removed from the eye. The fragmented nuclear material remaining in the eye is then removed by well know irrigation aspiration procedures. Although adequate initial containment and control of the nucleus is afforded by the Kramer patent, crushing very hard nuclei requires extreme force with little control or margin for error and leaves a significant percentage of the nucleus still in the eye after withdrawal of the instrument. For such reasons, a more controlled method of capturing and fragmenting the lens must be sought.
Many surgical instruments have been developed for very controlled capture and manipulation of tissues within body cavities. Some of these instruments incorporate wires that extend from distal ends to grab or contain objects. Itoh U.S. Pat. Nos. 3,739,784 and 3,791,387 disclose surgical instruments with distal single and multiple wire loops for capturing and cutting tissues within a body cavity. The multiple loop device has a wire with a pivotally attached loop allowing for longitudinal shifting of the wire in a tube. This permits the second wire to be bulged out from the loop to receive the tissue to be captured.
Dulebohn U.S. Pat. No. 5,176,688 discloses a surgical instrument with a single wire snare at its distal end. The distal end of the instrument is modified so that the cutting edges are not exposed to surrounding tissues, thereby protecting surrounding tissues from being damaged during insertion and while cutting with the instrument.
Grayhack et al. U.S. Pat. No. 5,098,441 disclose an instrument for containment and removal of calculi. The surgical instrument consists of an extendible central grasping device of a conventional "stone basket" type of expandable multiple wire loop system. The grasping device is surrounded by a smooth expandable outer tube. The grasping device captures the stone which is retracted within the smooth outer tube forming a protective closure to prevent injury when the stone is extracted.
Wechler U.S. Pat. No. 5,098,441 discloses a lithotriptor with a plurality of outwardly curved catch wires. The wires are constructed in a stranded fashion to achieve large load transfers while handling calculi.
Narayan et al., U.S. Pat. No. 5,176,688 discloses a surgical instrument for removing calculi from the body with a catch basket consisting of a plurality of wires that surround a reciprocating shaft. The reciprocating shaft extends into the cavity of the wire basket breaking up the captured stone.
Clement U.S. Pat. No. 5,197,968 discloses a surgical apparatus consisting of an expandable wire catch basket with an anvil at the distal end of the basket. A reciprocating cutting member is positioned so that when it is extended, it passes through the basket cavity and impacts the distal anvil, thereby cutting the contained tissue. Suction then removes the cut tissue from the body.
Gibbs et al., U.S. Pat. No. 5,330,482 disclose a surgical device consisting of a composite wire construction extraction device. The composite construction of the wire is intended to extend the operating life of the wire catch basket.
Bates et al., U.S. Pat. No. 5,496,330 discloses a surgical device for removing calculi. The device consists of a plurality of wires with pairs of wires formed along the turn of a helix. This construction allows for a greater number of contact points with the entrapped tissue.
These and other surgical extractors have certain common characteristics. Each retrieval basket comprises a plurality of wires which expand in a symmetrical fashion creating a retrieval basket. The expansion and contraction of the wire catch basket is controlled by means of a mechanism on the proximal end of the instrument.
Phacoemulsification is a more recent surgical method than standard extracapsular cataract surgery and utilizes ultrasonic energy to emulsify a cataract nucleus and aspirate the cataract from the eye through a smaller incision (2.5-3.2 mm) than extracapsular cataract surgery. The advent of foldable intraocular lenses to complete the surgery has resulted in sutureless surgery with virtually immediate visual and functional recovery. For these reasons phacoemulsification has become the most popular method of cataract surgery today. Nevertheless, phacoemulsification is very expensive and requires sophisticated equipment that demands significant expertise to operate safely, particularly in the setting of a mature hard cataract. Moreover, the equipment used for phacoemulsification is complex and expensive. For these reasons there remains a desire for simpler less expensive methods and devices for performing cataract surgery. Such a desired method would provide a surgical instrument for safe, controlled, uncomplicated, removal of the nucleus from the eye regardless of the maturity or hardness of the nucleus and could be inserted into the eye through a 3 to 5 mm incision and remove the nucleus, in its entirety, from the eye without enlarging the surgical incision.